Project Summary My long term goal is to lead a research group in a top tier academic institution in the pursuit of my interest: the genetic regulation of vascular development and disease, with a focus on the endothelium and hemodynamic activation. I am fascinated by the effects of blood flow on the vasculature and have focused on the transcriptional regulation of endothelial function for the past 10 years. I believe that in vivo genetics and imaging will be the key to understanding the complex interaction between the endothelium, blood flow, and recruited blood cells. This, in turn, is critical to understanding vascular development and diseases, such as aneurysms and atherosclerosis, which are driven by hemodynamic disturbance. I am committed to spending my life in this work. This award will provide critical training and development time to ensure my successful transition to an independent faculty position. In Richard Hynes' lab, under my F32 award, I examined the regulation of the Fibronectin transcript in response to low and disturbed flow in the arterial endothelium and uncovered a surprising splicing switch that resulted in the inclusion of two widely conserved alternative exons. Fibronectin is one of the most abundant extracellular matrix proteins in aneurysms. Using genetic models I showed that this splicing switch protects against hemorrhagic dissection of the arterial vessel wall under low and disturbed flow. Although a number of critical endothelial proteins are alternatively spliced, and alternative splicing programs are emerging as pivotal control mechanisms in other developmental processes, almost nothing is known about the regulation and function of alternative splicing in the arterial endothelium. To address this deficit, I will (Aim 1) examine i greater detail the mechanism(s) through which alternative splicing of Fibronectin protects against dissecting hemorrhage, and (Aim 2) exploit a database we have amassed, of alternative splicing events induced in the endothelium by macrophage recruitment under disturbed flow, to identify critical splicing factors and their functions in flow---driven inflammation. Richard Hynes (expert in extracellular matrix and Fibronectin biology) and Chris Burge (expert in genome---scale analysis of alternative splicing) will mentor my work during the K99 phase of the award. The congregation of talent in the splicing field at MIT will be an added benefit; Phil Sharp first discovered splicing here 30 years ago and it remains a focus of his lab and others nearby. The completion of these aims will add a new dimension to the genetic regulation of the flow---activated arterial endothelium, and enable the development of diagnostics and treatments for flow---driven vascular diseases through a deeper understanding of the basic biology.